AMD started delivering on their word of providing GPU specifications to the open-source community without a Non-Disclosure Agreement, and now with the 2007 X Developer Summit having come to a close, we asked several key members of the X.Org community on how they judge AMD's recent move. They were also asked if they believe NVIDIA will follow suit in helping the open-source community. Those that responded were David Airlie, Daniel Stone, Jerome Glisse, Stephane Marchesin, and Oliver McFadden. Mark Shuttleworth had also previously commented on AMD's efforts.

[q]"Looking into 2009, AMD will be coming out with Fusion and will likely need to give out at least some of the specs to it in order to gain traction in the cpu market and I think this may be preparation for it."[q]

That is basically what David Airlie was attributed as saying in the article

So the reason AMD started an open source GPU strategy was purely due to 2 things:

1.) Lost CPU sales due to lack of open source GPU support at an OEM level.
2.) Future CPU/GPU combination projects would require opening info on the GPU portion to allow uptake.